Nanocages 'cook' cancer cells

(Nanowerk News) Nanoscale cages constructed of gold atoms and targeted to cancer cells show a remarkable ability to kill tumors when irradiated with near-infrared light. Now, a team of investigators, led by Younan Xia, Ph.D., University of Washington in Seattle, has quantified how many targeted nanocages bind to an individual cancer cell and how much light is needed to kill the cells. These findings will help the investigators better plan future in vivo studies to determine whether gold nanocages can be used to treat cancer.

In 2005 Dr. Xia and his colleagues first created gold nanocages and targeted them to tumors using the same monoclonal antibody found in Herceptin®, which is used to treat certain types of breast cancer. At the time, the investigators showed that these nanocages bound tightly to targeted breast cancer cells. In the time since that initial report, the investigators have shown that these nanocages absorb near-infrared light and turn the absorbed energy into heat that can kill tumor cells. This current study, published in the journalACS Nano ("A Quantitative Study on the Photothermal Effect of Immuno Gold Nanocages Targeted to Breast Cancer Cells "), aimed to quantify this so-called photothermal effect to determine the optimal doses of both nanocage and light needed to effectively kill tumors.

To conduct this study, the investigators relied on a well-established technique known as flow cytometry, which can rapidly count the number of cells flowing through the instrument. They also relied on mass spectrometry to then quantify the amount of gold bound to a known number of cells. Using this approach, the researchers showed that an average of 400 targeted gold nanocages can bind to each cancer cell. The investigators note that knowing this number will enable them to calculate the dose needed to kill a tumor of a given size.

Next, Dr. Xia and his collaborators quantified how effective the nanocages were at killing tumors as they varied the intensity of near-infrared laser light shining on the cells and the time of exposure to the light. These experiments showed that cells binding to targeted nanocages began to suffer damage immediately when exposed to laser irradiation. This damage was irreversible when the power density exceeded 1.6 W/cm2. At this power level, maximal therapeutic effect was seen with a mere 5 minutes of irradiation.